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Impeller housing overheating


Skahamalibu

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I have a 2003 sportster with a monsoon 335 engine. The engine was running at around 100 degrees at the start of the season so I replaced the thermostat. The new thermostat worked well, the engine heated up to 160 degrees and held there. I just had the boat winterized and the mechanic said the housing over the impeller was running hot because the water does not begin to circulate until the temperature hits 160 degrees. He said there is a second thermostat below the top thermostat that opens to allow water to circulate and cool down the impeller. Is this right? Any idea why the housing over the impeller is getting so hot?

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I have a 2003 sportster with a monsoon 335 engine. The engine was running at around 100 degrees at the start of the season so I replaced the thermostat. The new thermostat worked well, the engine heated up to 160 degrees and held there. I just had the boat winterized and the mechanic said the housing over the impeller was running hot because the water does not begin to circulate until the temperature hits 160 degrees. He said there is a second thermostat below the top thermostat that opens to allow water to circulate and cool down the impeller. Is this right? Any idea why the housing over the impeller is getting so hot?

that whole "water does not begin to circulate until the temperature hits 160 degrees" does not sound correct, to me.

regardless of the temperature of the coolant, there is water flow through the raw water pump (driven by the impeller) to the t-stat housing because there is ALWAYS water through the t-stat housing into the exhaust manifold to keep the exhaust manifold and the rubber exhaust tubes fiberglass mufflers cool.

i agree that it sounds like you have a circulation problem. check the water input side of the transmission cooler to insure it is clear of debris/ trashed impeller parts. then i would check to insure that the hoses and valves that supply the raw water pump are free and clear. if those check out swell then the impeller is one of the few things left. i would replace the impeller AGAIN with a known NEW impeller. if that does not fix the problem then that known / new impeller will make a good spare for next season so the $$ isn't lost.

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Marinized engines incorporate a water bypass, mainly to keep water flowing through the exhaust manifolds to keep them within proper temperature ranges and this bypass allows water to constantly be pumped through the raw water pump. You can follow your water circuit and pretty easily identify the bypass components, there are many variations on the theme depending on who is the marinizer (Indmar, Mercruiser, PMC. . .). When you replaced the thermostat, did you ensure there were bleed holes in it? Some require them, depending on application, check the old stat for holes or just drill a couple of 1/8" holes in the stat to allow bleed water to pass through.

On the impeller, the primiary method of overheating is due to lack of inlet water. Running the boat out of the water, or with a failed Fake-a-Lake setup will allow the impeller to spin in a dry environment thus overheating the components and leading to failure. If done previous to your knowledge, that could be a source of trouble.

As mentioned, check for blockage at the trans cooler by removing the inlet side water hose and cleaning out any debris inside. Other blockages could lead to a similar problem, so if nothing there, check exhaust manifolds for blockage.

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that whole "water does not begin to circulate until the temperature hits 160 degrees" does not sound correct, to me.

regardless of the temperature of the coolant, there is water flow through the raw water pump (driven by the impeller) to the t-stat housing because there is ALWAYS water through the t-stat housing into the exhaust manifold to keep the exhaust manifold and the rubber exhaust tubes fiberglass mufflers cool.

i agree that it sounds like you have a circulation problem. check the water input side of the transmission cooler to insure it is clear of debris/ trashed impeller parts. then i would check to insure that the hoses and valves that supply the raw water pump are free and clear. if those check out swell then the impeller is one of the few things left. i would replace the impeller AGAIN with a known NEW impeller. if that does not fix the problem then that known / new impeller will make a good spare for next season so the $$ isn't lost.

Thanks for your answer. I can see the t-stat housing to allow water to go into the exhaust manifold. This is probably a dumb question but is there a thermostat in the t-stat housing or is it wide open. The mechanic that winterized the boat thought that there was a second thermostat but that does not make sense to me. I'm thinking there is a blockage at either the transmission cooler or further back at the transmission.

Thanks,

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Which impeller housing is he talking about?

The typical impeller is rubber and sits directly on the crank & draws water from the lake into the trans cooler & then into the engine. Once the engine is full the lake water is typically redirected to the exhaust risers. The water is circulated within the engine by a water pump that is nearly identical to a car's water pump & also contains an impeller that is not typically replaceable.

The thermostat will allow the hot water circulated within the engine out & it will be replaced by cool water supplied by the impeller.

There is/should be a thermostat within the housing.

The lake water should keep the impeller housing cool, but if there is a blockage somewhere - or the impeller is not seated fully - the impeller housing may heat up. I would think if you're getting that little flow, then the engine would overheat too. How much water are you getting out of the exhaust when it's run on the hose or fake-a-lake?

You may want to consider finding a mechanic with a little more specific knowledge of these marinized engines & systems.

Edited by wienrdog
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Thanks for your answer. I can see the t-stat housing to allow water to go into the exhaust manifold. This is probably a dumb question but is there a thermostat in the t-stat housing or is it wide open. The mechanic that winterized the boat thought that there was a second thermostat but that does not make sense to me. I'm thinking there is a blockage at either the transmission cooler or further back at the transmission.

Thanks,

"blockage at the transmission cooler" is a real possibility (that's why i suggested "check the water input side of the transmission cooler to insure it is clear of debris/ trashed impeller parts" in my first post within this thread.

there isn't any water "further back at the transmission" so that is NOT the right direction to head in diagnosing your problem.

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